Dual purpose voltmeter range attenuator



Aug. 16, 1949. R. w. GILBERT DUAL- PURPOSE VOLTMETER RANGE ATTENUATOR Filed March 29, 1948 Patented Aug. 16, 1949 "Nanettex L, acor oratienof r-New Jersey .naaat at ra, 1921as sriti m.inert '4 name; (cent- 595i "J'Th'i's invention relates to vane-eta range at;- tenuatcrs or resistance .fi'letwbTK Sj "adiustaible "to aiterthemeasdring range for mitmeteraandm'ore particmarly "to a dual purpose range attenuator for usewitn a vacuum tube voltmeter "which is alsopp'er'able as a direct indicating 'voitineter. 'I nighiriiputfinpeaanee:vaetidm rdbeivmtf etersfit customary to use; a shunt tag'e tinde attenuator." franc-sens pr fe' tnpm erititnen grrest i'easib're inputimpedanee usua-ny 'de'terffiined'by the upper limit erresistance to which accurate resistors can be armractured; and the si'fiiiit type Ioi -divider presents tne'entire orall "resistors as tireinput 1m,- ipecancej. 1Tlie' lowest "measuring range is obtainedtneentrre mirage-drop across the divideris impressed upon trre v acuurh tube 93h fplifi'e'r' system; and higher finea'sunng ranges fare obtained by adjustment or a tap switch :to im ress-- only a selected fraction er the full i drop upon the vacuum The shunt type of voltage divider is the most efiectiv'etype of neat network where high input impedance on all measuring ranges is a primary object. o however, in portable vacuum tube vortm'eters it is also desirable to arrange the' 'circu'ittobe usable as a standard direct indicating voltmeter when service power 'for operation of the instrument-amplifier is not ataii'ebie. Unfortunately the shunt 'typeof divider i -s not iqsable the indicating instrument requires current for its operation, and a second divider of the series type is customarily necessary where this type of dual operation is desired. In conventional practice the shunt and the series dividers would be physically separate devices, and the dual operation feature would require two entirely separate sets of range resistors.

Objects of the present invention are to simplify the construction of the range attenuators of dual purpose voltmeters by employing a single set of resistors for both the shunt and. the series voltage dividers. An object is to provide a dual purpose range attenuator including a plurality of serially connected resistors, two sets of switch contacts connected to the terminals of the several resistors, the connections of the sets of contacts being reversely arranged, and switch blades ganged for simultaneous adjustment with respect to the sets of switch contacts, one switch blade being connected to an input terminal and the other switch blade being connected to the input to the vacuum tube voltmeter. A further object is to provide a dual purpose range attenuator as.

time amplifier? system.

' macaw-eta in which the resistors have such relative values that each'adjustment time range chang switches conditions the a paratus for the measurements by the vacuisameran e ofv'olta'ge p H the direct indicating um tube voltmeter and ter. r

These and other cbiects and the advantages ot the invention will fb'eanparent from the following specification when taken with the [accompanying drawings in which: f

Fig. 1 is a circuit diagram of a dual voltage range attenuator and voltmeter assembly embodying the' invention;

Fig. 2 is a circuit niag'rarnef nnother embodiment .in which a single meterzis employed for direct voltage, measurements-aha vacuum tube voltmeter'rneas'urenients. g

In the Fig. 1 diagram, the reference'characters Rl to R6 identify a plfir aliit y'roin'esistors connectedin series vz'ith e'a other and with a meter V which has inter fl' res'istance Ri, as indif v A cross the schematically shown instrument A series of taps or switch contacts are connected to the outer terminals of resistors R to respectively, and apooperatingswitch blade 10 whicl-i is adzlustable along the contacts -l fi is connected by a lead 14 to an :inputtermi-nal; t2. Theother input terminal -l dis-connected by-a lead {4 tothe terminal of meter v "opposite-that to which :the :resistor connected. Inputyoltages E which are applied to input terminals l2, l3 may be measured in different ranges according to the relative values of the several resistors and the adjustment of the switch blade H! with respect to the taps or contacts l-G. The lowest measuring range is obtained when the switch blade l0 engages the contact l to include only the resistor RI in series with the meter V, and progressively higher measuring ranges are obtained by shifting the switch blade H) to include additional resistors in series with the meter.

A second set of switch contacts l'-6' is connected to the outer terminals of the resistors Rl to R6, and these contacts are reversely connected to the resistor terminals, i. e., contact I is connected to the outer terminal of resistor 8, contact point 2| and the common terminal I3 is indicated on a meter V which preferably is identical with 1 the meter V. V I

It will be apparent that a common graduated scale of measuring ranges for direct voltage measurements and vacuum tube voltage measurements is possible only when the values of the several resistors Rl to R1 are related in the novel manner 7 contemplated by the invention. For a common scale of voltage ranges it is essential that the range complements form a symmetrical progression, 1. e. that the ratios between adjacent ranges are the same progressing downward from the highest range and upward, from the lowest range. As indicated by the values appearing on the range scale .I 8, the voltage ranges are:

Other symmetrical scale ranges are possible, for example:

For a voltmeter of 10,000 ohms per volt and the indicated voltage ranges, the values for the several resistors are:

R|+Ri=30,000 ohms R2 -90, 000 ohms 'R3=180,000 ohms R 4=900,000 ohms R5=1.8 megohms R6,=9.0- megohms R1=3.0 megohms The total input impedance of the vacuum tube voltmeter for these resistor values is megohms.

The dual purpose measuring apparatus may be further simplified by providing a switch S, as shown in Fig. 2, for connecting a meterV in series with the resistors R| to R6 for direct voltage Number uring devices fall within the spirit and scope of the invention as set forth in the following claims.

Iclaim: l. A dual purpose voltmeter comprising a plurality of serially connected resistors, two sets of switch contacts reversely connected to the junctions of said resistors, switch blades ganged for simultaneous adjustment with respect to the sets of switch contacts, a meter connected between one end of the serially connected resistors and a common input terminal, a second input terminal connected to one of the switch blades, an alternative second input terminal connected to the other end of the serially connected resistors, and a vacuum tube voltmeter connected between the common input terminaland the other switch blade.

2. A dual purpose voltmeter as recited in claim 1, wherein the values of said serially connected resistors are so'related that the measuring ranges of the voltmeter as established by adjustment of the switch blades form a symmetrical progression.

3. A dual purpose voltmeter as recited in claim 2, in combination with a single graduated scale of voltage measuring ranges, and an index mark ganged to said switch blades and movable along said graduated scale.

4. A dual purpose voltmeter as recited in claim 1, in combination with switch means for connecting said meter inserie's with said resistors or, alternatively, in the output circuit of said vacuum tube voltmeter. V V

-' V J ROSWELL W. GILBERT.

REFERENCES CITED wThefollowing references are of record in the file of this patent:

FOREIGN PATENTS Country Date 164,792 'Germany -QJune 28, 1904 

